This invention is applicable in a real time system including an external device, interface hardware that automatically controls handshake protocol with the external device and a host processor. In this real time system the external device control protocol is mainly handled by the interface hardware because high speed is needed to provide real-time performance. The interface hardware access is much faster than access by a software program driving the host processor. Thus the host processor is not effective for controlling the handshake protocol due to wait sequences for the external device.
This system may breakdown once the handshake protocol stops due to trouble with the external device. Once this breakdown occurs, it may take 10 to 20 seconds recover. Such system breakdown causes problems.